Gas turbine engines, especially those mounted on aircrafts, are known to operate under a wide range of conditions and power requirements. In a typical cycle, a gas turbine engine rotates at high speeds during takeoff and climb segments, while running at lower speeds during other segments, such as warm-up, taxiing, cruise and descent. Gas turbine engines must also operate under various temperatures, pressure and air speeds throughout a same engine cycle. All these requirements generally lead to various design compromises so that the engines can deliver a good performance at all times. As with all optimization, however, at some points during an engine cycle, one portion of an engine may be capable of generating more power than is required with reference to the selected operating point of one or more portions of the engine. In other words, in optimization, sometimes excess capacity in the engine is left unused.
U.S. Pat. No. 5,694,765 to Hield et al. discloses a mechanism by which power may be transferred from one gas turbine engine spool to another within a multi-spool engine. However, there is a continuing need to provide an improved engine design and method by which engine power can be transferred and used optimally.